Drug repositioning or repurposing has received major interest in the past years. This approach increasingly enables scientists to discover potential pharmacological targets and to identify “new targets” of known drugs. It is found to be an attractive approach for efficient drug discovery and development, taking advantage of already available preclinical and clinical knowledge, thus allowing for considerable shortcuts in many steps in the drug development process. One important example of drug repositioning is colesevelam, originally developed as an adjunct to reduce low-density lipoprotein cholesterol (LDL-C) but now it is approved as a hypoglycemic agent for type 2 diabetes mellitus. Therefore, keeping the importance of this approach, our drug screening project is aiming to identify new drugs for lead optimization for different ailments. In the present studies, urease inhibitory assay was employed to evaluate the activity of (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid.
(2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid is an angiotensin-converting enzyme (ACE) inhibitor, and approved as drug (Captopril) for the treatment of hypertension, and heart failure. Captopril was developed and marketed by US drug company, “Squibb and Sons Pharmaceuticals”. Its discovery and development was based on concepts pioneered by Nobel Laureate Prof. John Vane.
Besides its blood pressure-lowering properties, (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid has various biological activities, such as immunomodulatory, beneficial effects on rheumatoid arthritis, prevention of complications in insulin-dependent diabetes mellitus, and anti-inflammatory properties (in schistosomiasis). Additionally it is found to be effective in lupus diseases, and autoimmune encephalomyelitis (EAE). Captopril was found to be capable of suppressing the production of monocytes/macrophage-derived proinflammatory cytokines (e.g. tumour necrosis factor (TNF), IL-1, IL-6, and IL-12). These immunomodulatory actions of captopril were due to different mechanisms, such as anti-proliferation, anti-oxidant, inhibition of metalloproteases, and elevation of prostaglandin. It is reported that these properties are related to the presence of thiol groups in its structure. (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid has recently been found to inhibit Fas-induced apoptosis in human activated T cells and lung epithelial cells. It is also known to be used for the treatment of cysteine stones. The drug has a cysteine binding thiol group, resulting in the formation of captopril-cysteine complex, which is about 200 times more soluble than cysteine. Dose of 70-100 mg per day effectively reduces the formation of cysteine stones. Therefore, it is considered as a drug of choice in cysteine stone patents with history of hypertension.
Urease (amido-hydrolase, EC 3.5.1.5) is a large multimeric, Ni+ containing metallo-enzyme. Ureases of plant and fungal origins are homo-oligomeric proteins, while the ureases of bacterial are heteropolymeric proteins. Biologically, it catalyzes the hydrolysis of urea into ammonia and carbamate. At physiological pH, carbamate spontaneously hydrolyzes into carbonic acid and ammonia. It plays an important role in nitrogen cycle, as it supplies nitrogen for seed germination and for the growth of microorganisms by facilitating breakdown of urea into ammonia. Beside this physiological role, it also has a pathological role in a wide range of diseases, such as urolithiasis, hepatic encephalopathy, hepatic coma, pyelonephritis, urinary catheter encrustation, gastritis, peptic, duodenal ulcers, and gastric cancers. Ammonia (released by the hydrolysis of urea) is one of the well-known causes of hepatic encephalopathy. Apart from causing diseases to human, it also causes several environmental and economic hazards in agriculture. Urease positive soil bacteria release ammonia in high quantity which not only deplete the urea, but also cause toxicity to plants. This scenario therefore demands discovery of effective inhibitors of urease enzyme.
Urease inhibitors are also required as drugs for the eradication of Helicobacter pylori, for the treatment of peptic ulcers, and other diseases, caused by ureolytic bacteria. Clinically used inhibitors against this enzyme include hydroxamic acid, bismuth complexes, and imidazole classes. However, these medicines have proved to be largely ineffective, and only a few have been approved for the use at clinical level. Search for new and effective inhibitors of urease is thus vigorously pursued in pharmaceutical research.
During the current study, Jack bean (Canavalia ensiformis) urease was used for in vitro biochemical evaluation, whose active site resembles to that of bacterial ureases with a bi-nickel nuclear center. The metallo-center comprises of two Ni+2 ions, bridged by a carbamylated lysine residue and water molecule. One Ni ion is linked with two histidine residues and a terminal water molecule, while the second Ni ion is linked with the histidine residues, one aspartic acid residue, and water molecules. The mechanistic studies were carried out to determine the binding mechanism of (captopril) to urease.